1. Field of the Invention
The invention relates to connector devices for integrated circuit packages and more particularly to a high density double contacting connector assembly for leadless integrated circuit packages having automatically preloaded contacts and a probing or testing facility.
2. Description of the Prior Art
Connector packages for leadless integrated circuit packages are well known in the art. These packages generally include a one or two piece header unit having two parallel rows of linearly disposed contact terminal cavities formed therein for reception of spring-type metal contacts. Due to the increasing density of large scale integrated circuit devices (LSIs) it is common to encounter such devices having 50 or greater terminal pads disposed thereon. Connection to these pads requires a high degree of accuracy in fabrication and alignment of the various components of a leadless LSI package connector. The circuit package may be connected to a printed circuit board by means of solder tails which project downward to fit through via holes formed on the printed circuit board. However, such schemes have caused considerable problems since the via holes in associated conductor paths on the circuit board must be spaced on 0.050 inch centers. it has been proposed to lessen the contact and conductor tolerances by providing a "double-contacting" connector package. Such a package includes terminal pads on the underside of the connector which rest on narrow conductive areas formed on a printed circuit board, the package being mounted on the circuit board by means of a bolt or screw fastener. Thus, the necessity of forming closely spaced via holes on the board is eliminated. However, such schemes have fallen short in that they have required a considerable amount of the header material to be used to provide dielectric and mechanical isolation between the terminals. Such prior art schemes have failed to provide for adequate and automatic preloading of the terminal itself when the connector package is assembled. Preloading a terminal allows a force to be present upon the instant of contact of the LSI terminal pad with the contacting portion of a connector terminal, thus insuring good electrical conductivity since proper terminal contact-to-IC package pad pressure is available the instant the LSI package is mounted onto the connector package. Furthermore, preloading allows a certain amount of beneficial self-wiping action by the contacting portion of the connector portions.
Prior art spring-type contact terminals have been formed in roughly "C" and "S" shaped configurations of strip-like spring metals of various types. Generally, such contacts have been formed from long pieces of narrow conductive metal strips or wire, such as shown in U.S. Pat. Nos. 3,955,867, 4,052,118, 4,050,755, 3,953,101, 3,933,384, 4,008,938, 3,940,786, 3,982,159, 3,851,491, and 3,873,173. However, such terminals are difficult and expensive to fabricate since the compound curves needed to insure uniform spring pressure from terminal to terminal are difficult to form reproducably and require special metal forming equipment. Additionally, after numerous insertion-removal cycles of an LSI package in a particular connector assembly, these bent strips will tend to weaken along their bends, thus lowering the spring pressure and contact pressure below desirable limits. Additionally, where the lower circuit board contacting portion is also formed of strip-like metallic material, such contacts have tended to be easily damaged or bent during fabrication, requiring much manual labor to straighten them before the connector can be mounted on a printed circuit board. It will be noted that these prior art terminals are usually arranged such that the width of the terminal is aligned horizontally, thus imposing the requirement that each terminal receiving cavity be at least as wide as the width of the terminal. Such prior art arrangements limit the number of terminals which can be placed with a given size of connector package.
It has been proposed to lessen the spacing requirements of the terminals by forming them of stamped sheet metal and mounting them vertically edgewise, as shown in U.S. Pat. No. 3,871,736. Finally, though it has been proposed to include probe holes associated with each terminal to allow testing of a completed connector-LSI package assembly, such as shown in U.S. Pat. No. 3,955,867, such structures have suffered from the disadvantage that contact must be made against a bent strip conductive metallic material which is prone to metal fatique after numerous probing operations. Such prior art probing terminals will tend to permanently "give" or flatten out of reach of the probe tip after a while, resulting in loss of the probing facility at that particular terminal.